Coding & Algorithms Interview Questions
Practice 3,013 real Coding & Algorithms interview questions for 2026. Coding & Algorithms interview questions for top tech firms like Meta, Amazon, Google, Uber, and TikTok — real questions from actual interviews with detailed solutions — to power your interview preparation. This collection is sharply focused on algorithmic patterns (arrays, strings, sliding windows, trees/graphs, dynamic programming, greedy, two-pointers, and hashing), clean, review-ready code, and the explanation skills that distinguish hires. In 2026 expect familiar medium-to-hard problems plus newer twists: AI-enabled or multi-file coding rounds at some companies, more emphasis on explainability and edge-case reasoning, and occasional real-world performance constraints (streaming, concurrency, memory limits). Interviewers evaluate problem framing, algorithm choice, complexity trade-offs, test-case thinking, and communication under time pressure. Best prep mixes pattern-based practice, timed mock interviews, code-review style polishing, and rehearsed explanations of complexity and tradeoffs. Focus your last-mile prep on writing correct, readable code quickly and on explaining why your solution is robust and efficient for production scenarios.
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Print a binary tree as aligned text
Implement a function that prints (or returns) an ASCII layout of a binary tree. Requirements: - Each node has a string value (assume it contains no sp...
Count User Journey Prefixes
You are given a list of user activity logs. Each log record has the form [user_id, timestamp, action]. Example input: `text logs = [ [100, 1, "A"], ...
Implement LRU and LFU caches
Implement two in-memory cache classes with fixed capacity: 1. Recent-use cache - get(key): return the value for key, or -1 if the key does not exis...
First Word Matching Each Prefix Query
You are given a list of words (the dictionary) and a list of queries, where each query is a string prefix. For each query, return the index (0-based, ...
Solve String Arrays and Row Deduplication
You are given the following independent coding tasks. For each task, write clean production-quality code, handle edge cases, and state the time and sp...
Insert parentheses to minimize expression value
You are given a string expression of the form A+B, where A and B are non-empty strings of digits (no digit is '0'). You must insert exactly one pair o...
Predict most likely next word from training data
You are given tokenized training data consisting of multiple sentences (each sentence is a list of words). Build a lightweight model/data structure th...
Solve four algorithmic coding tasks
You are given four independent coding tasks. They may be solved in any order, and partial test-case credit is awarded for each task. The tasks are rou...
Implement Safe Average Function
Write a Python function average(values) that returns the arithmetic mean of a list of numbers. Requirements: - If values is empty, return 0. - The inp...
Reconstruct DNA from tagged fragments
You are given a list of DNA fragments. Each fragment is represented by a Sequence object containing two endpoint labels and a DNA string payload. Your...
Solve interval, grid-fill, and heap tasks
You are asked to solve the following algorithmic problems. Problem 1: Concurrent users from online intervals You are given n inclusive time intervals ...
Find Unique Target-Sum Pairs
Given an integer array nums and an integer target, return all unique pairs of values whose sum equals target. Requirements: - Each returned pair shoul...
Determine Safe Bomb Defusal
You are given a finite state machine representing a bomb defusal process. - Each state is represented by a string. - initialState is the starting stat...
Solve SQL and PySpark Data Tasks
Complete the following two data engineering coding tasks. Part A: Detect repeated crypto-transfer patterns in PostgreSQL You are given a PostgreSQL ta...
Implement an in-memory database with TTL and backup
In-Memory Database (Levels 1–4: TTL and Backup/Restore) Implement an in-memory database that stores records identified by a string key. Each record co...
Compute servers needed for daily recurring jobs
You operate a cluster of identical servers that run recurring daily jobs. For a single day, you are given a list of job execution intervals. Each inte...
Calculate Transaction Fees
You are building a payment processor. Each transaction has an amount in cents, a payment type, and a payment status. The platform charges a percentage...
Implement Rate-Limited Wikipedia Crawler
Implement a rate-limited Wikipedia crawler. You may use an AI coding assistant during the interview, such as Cursor or Claude Code. You are expected t...
Design log queries and a buffered writer
Part A — Log store with time-range queries: Implement a data structure that ingests log entries with ISO-8601 timestamps (e.g., YYYY-MM-DD HH:MM:SS) a...
Find the Best Commute Mode
You are given a 2D grid representing a city commute map. The grid contains exactly one start cell S and exactly one destination cell D. Each other cel...